The present invention relates to an optical encoder for detecting the position, the movement speed, the moving direction and the like of a moving object with use of a light receiving element, and more specifically relates to an optical encoder which is preferably used for, for example, printing presses such as copying machines and printers, as well as FA (Factory Automation) equipment.
Conventionally, an optical encoder has been proposed in which a plurality of light receiving elements are placed in an array direction of the slits of a rotor at intervals of ¼ of the array pitch of the slits and in which output signals of these light receiving elements are compared so as to obtain rotation information with high reliability (JP S59-40258 A).
In an optical encoder disclosed in JP 2005-61896 A, a method for enhancing the precision of detecting the movement amount of a moving object by generating and outputting triangular waves is employed.
It has been disclosed in JP 2000-121390 A that pulse conversion is applied to an A-phase signal and a B-phase signal, which have phase difference of 90 degrees, so that these signals are outputted as one A/B-phase pulse signal which is PWM-modulated corresponding to the moving direction of the scale, as a result of which the A-phase and B-phase measurement pulse signals can be outputted with one transmission line.
It has been disclosed in JP S60-88316 A that two phase outputs from a rotary encoder are converted to get counter pulses corresponding to two phases, and one counter pulse is phase-inverted and is added to the other counter pulse, so that signals can be transmitted with a single output signal line.
In the optical encoder disclosed in JP S59-40258 A, the relative position change and the moving direction of a moving object (rotor) are detected with use of two output signals of A-phase and B-phase which are different in phase from each other by 90 degrees.
However, in the optical encoder of JP S59-40258 A, two outputs are provided and therefore interconnections for two outputs are required, which makes the optical encoder lack in simplicity of the signal output interconnections and thereby makes the optical encoder unsuitable for pursuit of miniaturization of a mounting area. Moreover, since the timing of two output signals which should have phase shift of 90 degrees may be changed due to the difference in length of two output interconnections and to the influence of noise applied to each interconnection and the like, an output method with higher reliability is necessary.
In JP 2000-121390 A, pulse conversion is applied to an A-phase signal and a B-phase signal which have phase difference of 90 degrees, so that these signals are outputted as one A/B-phase pulse signal which is PWM-modulated corresponding to the moving direction of the scale.
However, while in the case of a moving object which constantly moves at a fixed cycle, it is possible to detect the moving direction with a PWM (Pulse Width Modulation) signal, in the case of a moving object which does not move at a fixed cycle, it becomes difficult to detect the moving direction of the moving object with high precision due to the pulse width of an output pulse and to the influence of jitter on output components. Moreover, in a signal composed of signal components of two phases, the number of counts of the moved positions in one cycle is only for one phase, and therefore the resolution is also reduced by half compared to the resolution in the optical encoder of JP S59-40258 A.
Moreover in JP S60-88316 A, one of the counter-pulse signals of two phases acquired from the rotary encoder is phase-inverted before these two signals are added together so as to achieve transmission of two signals with a single output signal line. However, as with the case of JP 2000-121390 A, the resolution is reduced by half, which makes it impossible to acquire relative position information with high precision.
Further, it is aimed in both JP 2000-121390 A and JP S60-88316 to reduce the total number of interconnections by signal processing, though devices such as counters, pulse modulators and oscillators are needed. This not only limits the available frequencies but also requires synchronization with an output section and complicates the configuration, which makes it difficult to miniaturize the portion where an encoder module is mounted.
Further in JP 2000-121390 A, PWM modulation is performed under microcomputer control corresponding to the movement information on the moving object. In short, since the PWM modulation is applied depending on the processing speed of the microcomputer or the frequency of an internal oscillator, it is difficult to determine the moving direction at the moment the moving direction of the moving object changes.
Similarly in JP S60-88316 A, the allowable cycle of the moving object depends on the frequency of oscillators. Therefore, although increasing the frequency of the oscillator makes it possible to cover a wide frequency ranges, consumed electric current is increased and therefore this solution is not suitable for practical use.
Moreover, although it is aimed in both JP 2000-121390 A and JP S60-88316 to reduce the total number of interconnections by signal processing, devices such as counters, pulse modulators and oscillators are needed, and this requires synchronization with an output section and thereby complicates the configuration. Consequently, it becomes difficult to miniaturize the portion where an encoder module is mounted.
Also in the optical encoder disclosed in JP 2005-61896 A, as with the optical encoder disclosed in JP S59-40258 A, it is necessary to use two phase outputs for detecting the moving direction.